Meetings

ancing filters, including the three-foil technique, has been discussed in detail by Young (1963). If the three-foil technique is to be used, the second bracket may be fitted with an adjustable filter holder in addition to the fixed filter. Filter and attenuator-position feedback signals are generated by a system of light sources and photocells. Each filter bracket has a wing with two holes [4] that moves in a slot cut in the electrical hardware mounting bracket [16]. Two light sources [18] are mounted in the block on one side of the wing with two photocells [14] directly opposite them. The holes are arranged so that one of the photocells is illuminated when the filter bracket is in the 'up' position while the other is illuminated in the 'down' position. The size and location of the holes in wings are such that, unless the filters are in their proper position to within 0.030 inch, neither photocell will be conductive. The balanced filter device described here may be interfaced with an automatic control system in one of several ways. In our laboratory, the interface is with a Humphrey Electronics Model 901OR step scanner which both prints the output data and punches it into paper tape. On command from the programmer control, appropriate signals are sent to the balanced-filter box to move the filters into the required positions. At the same time, signals are generated which set up a conditional filter-position printout. These filter-position printouts occur only if the correct feedback signals have been received from the photocells. If the correct feedback is not received, the filter position printout is replaced by an error message. With the attenuator and balanced filter data, scaling of attenuated data, and identification and correction of erroneous data may be readily performed on a digital computer. If an automatic control system is not available, the box may be operated manually with a simple circuit consisting of the appropriate power supply, toggle switches to position the filters and attenuators, and lights operated by the feedback system to show their positions. Complete engineering and electrical drawings of the balanced-filter box and specifications for all commercial components may be obtained from the authors.


I41
surface was smooth and shining; they were slightly raised above the skin-level, and were round, polygonal, or squarish. There was no history or suspicion of syphilis.
Dr. Prowse brought before the Society two cases of tumour of the pons (which will be published in full in the September number), and also the case of a young woman aged 19, who was admitted to the Infirmary on January 7th, 1891, and died on January 12th. There was a history of cyanosis and dyspnoea for some years; the legs had been oedematous for three months. The apex-beat was displaced to the left, and there was epigastric pulsation, presystolic bruit, and reduplicated first sound. Haemoptysis supervened, and the dyspnoea became so urgent that it was decided to aspirate the right ventricle. This was accordingly done, and twelve ounces of blood withdrawn with great relief. A few hours later, however, the distress was as great as before, and death occurred rather suddenly. At the post mortem examination the mitral orifice was found greatly stenosed.
Mr. Pickering read notes of two cases of septic thrombosis of the lateral sinus. (These will be published in full in September.) Dr. Edgeworth gave an account of the chief phenomena of hypnosis, and subsequently demonstrated these on a boy. He first explained the methods used to produce the hypnotic state, its various stages, and the alterations which take place (independently suggestion) in voluntary movements, sensation and memory. He then stated the results of hypnotic and post-hypnotic suggestion on these faculties. These phenomena were illustrated on the subject. Votes of thanks were passed to the British Medical Association and to R. B. Ruddock, Esq., for their generous and important gifts to the Library of the Society.
Dr. Watson Williams was requested and consented to act as delegate for the Society at the Congress for the Study of Tuberculosis, to be held in Paris in July next.
Dr. Michell Clarke read a short account of, and showed specimens from, three cases. (1) From a patient who died in the Hospital, under Mr. Dobson's care, from gangrene of the left foot and lower part of leg. She had left hemiplegia. There was no rheumatic history, and no murmur could be detected over the heart. At the post mortem examination, a large thrombus was found obstructing the abdominal aorta at its bifurcation. There were clots also in both common and external iliacs, and the right middle cerebral artery was blocked by an embolus; there were several infarcts in the left lung and kidney. The right lung was completely collapsed, appar- posterior part of the right internal capsule. This had caused left hemiplegia and hemianesthesia. The symptoms pointed to vascular obstruction from thrombosis.
The man died from a large fresh hemorrhage from the lenticulo-striate artery. He was the subject of Bright's disease. ("3) Specimen of duodenal ulcer, the base of which was adherent to, and formed by, the gall-bladder. The latter contained cholesterin stones.
There were no symptoms caused by the ulcer.
Dr. Markham Skerritt showed (1) Portion of a sarcoma of the right lung, which weighed 164 ounces, from a lad whose left thigh had been amputated for similar disease a year previously. The growth simulated some of the physical signs of extensive effusion, e.g. displacing heart, etc. It also pushed the diaphragm down three inches below the ribs, and could, therefore, be plainly felt in the left hypochondriac region. (2) A tumour of the right kidney, which microscopical examination showed to be an epithelioma with typical "nests" and penetrating columns ot cells. The growth appeared to start from the neighbourhood of a calculus which obstructed the ureter about three inches below the pelvis. The symptoms had lasted five months.
Mr. C. A. Morton showed (1) A specimen of syringo-myelocele. The cavity was directly continuous with the central canal of the cord above; below, the cord divided into two hollow parts. Nerves could be traced in the walls of the sac. Mr. Morton commented on the rarity of this condition of division of the cord. (2) The bones of an infant, the ends of which showed peculiar changes, probably syphilitic in nature. The epiphyses were separated.
Dr. George Parker exhibited an aneurism, the size of a hazelnut, situated on the basilar artery at its upper part. The case was remarkable from the complete absence of any localising symptoms.
No cause for its occurrence was ascertained.